Vision loss linked to dementia
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A large-scale study has identified poor eyesight and high cholesterol as two new risk factors for dementia. The study claims that eliminating these factors, along with 12 other previously recognized factors, could prevent almost half of all dementia cases worldwide. However, some of these factors are difficult to eliminate, and genetics and advanced age remain the biggest risk factors for developing dementia.
“Dementia may be one of the most significant health threats facing the public,” says Gill Livingstone, from University College London, “so the fact that we have the potential to turn this around and significantly reduce the number of people affected by the disease is incredibly important.”
A 2020 study identified 12 potentially modifiable risk factors for dementia, including hearing loss, depression, smoking, high blood pressure, heavy alcohol consumption, obesity, air pollution, traumatic brain injury, diabetes, social isolation, physical inactivity and lack of education.
Livingstone and 26 other dementia experts from around the world updated the list based on the latest evidence, retaining the 12 risk factors but adding two new ones: high levels of low-density lipoprotein (LDL) “bad” cholesterol before the age of 65 and untreated vision loss in later life.
The researchers included high LDL cholesterol based on several new findings, including an analysis of 17 studies that followed almost 1.2 million British participants under the age of 65 for at least a year.
The study showed that for every millimole per liter (mmol/L) increase in LDL cholesterol, the incidence of dementia increased by 8 percent. Another similarly sized study found that high LDL cholesterol levels (above 3 mmol/L) were associated with an average 33 percent increased risk of dementia. This risk was most pronounced in people with high LDL cholesterol levels in midlife. “So it really depends on the time period,” Livingston says.
The researchers suggest that this association may mean that excess cholesterol in the brain increases the risk of stroke and contributes to dementia. Cholesterol has also been linked to the buildup of beta-amyloid protein plaques in the brain, which is linked to Alzheimer’s disease.
Untreated vision loss was included as a risk factor in an analysis of 14 studies involving more than 6.2 million older adults who were initially cognitively healthy, which showed it increased the risk of developing dementia by 47% after up to 14.5 years. Another analysis showed the risk was mainly due to cataracts and diabetic complications. “We think the risk of vision (loss) is because it reduces cognitive stimulation,” Livingston says. Some research suggests that such stimulation makes the brain more resilient to dementia.
The researchers then used their model to estimate what percentage of dementia cases worldwide could be prevented if each of 14 modifiable risk factors were eliminated. They found that hearing loss and high cholesterol had the greatest impact, each contributing about 7 percent of dementia cases, while obesity and excessive alcohol consumption had the least impact, each contributing 1 percent. If all factors were eliminated, the team estimated that about 45 percent of dementia cases could be prevented.
But just because these factors are associated with dementia doesn’t mean they cause it, says Dylan Williams of University College London, who was not involved in the report: “So targeting these factors with interventions may not prevent as much disease as we would hope.”
These estimates are only population averages and don’t capture individual-level risk, Williams says. So removing all factors from your life wouldn’t necessarily halve your risk of dementia, which is heavily influenced by genetics and age. Eliminating many of these risk factors, like air pollution or lack of education, would also require public health interventions rather than individual changes, Williams says.
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